Piloted flameholder construction

ABSTRACT

A piloted flameholder construction having a plurality of combustion zones to which are supplied fuel and air to support combustion therewith. Combustion gases from at least one of the combustion zones are then supplied to a plurality of flameholders thereby improving combustion efficiency and stability of the flameholders. This flameholder construction is particularly adaptable for use in a ducted fan gas turbine engine. This application is reported as a Subject Invention under Government contract AF33(657)14903.

United States Patent 1 1 Marshall et al. Apr. 2, 1974 [5 PILOTEDFLAMEHOLDER 3,274,776 9/1966 Ravel 60/39.72 R

CONSTRUCTION [75] Inventors: Richard L. Marshall; Dennis J. PrimaryExaminer-Samuel Feinberg Sullivan, both of Manchester, Conn. Attorney,Agent, or Firm-Jack N. McCarthy [73] Assignee: United AircraftCorporation, East Hartford, Conn. [57] ABSTRACT [22] Filed: Mar. 18,1971 [21] APPL NO: 125,882 A piloted flameholder construction having aplurality of combustion zones to which are supplied fuel and air RelatedApplication Data to support combustion therewith. Combustion gases [63]Continuation-impart of Ser. No. 741,159, June 27, from at least one ofthe combustion zones are then 1968, abandoned. supplied to a pluralityof flame-holders thereby improving combustion efficiency and stabilityof the [52] [1.8. CI. 60/39.72, 60/224 flameholders. This flameholderconstruction is pani [51] Int. Cl. F02g 1/00 ularly adaptable for use ina ducted fan gas turbine en- [58] Field of Search 60/39.72, 39.74, 261,39.65 gine.

, This application is reported as a Subject Invention [56] ReferencesC'ted under Government contract AF33(657) 14903.

,UNITED STATES PATENTS 2,679,137 5/1954 Robert 60/39.65 13 Claims, 5Drawing Figures PILOTED FLAMEI-IOLDER CONSTRUCTION CROSS-REFERENCE TORELATED APPLICATION This application is a continuation-in-part ofApplication Ser. No. 741,159 filed June 27, 1968 for PI- LOTEDFLAMEI-IOLDER CONSTRUCTION, now

abandoned.

BACKGROUND OF THE INVENTION This invention relates to a pilotedflameholder construction, one configuration thereof being particularlyadapted for adding heat to the bypass air of a fan engine therebyincreasing the overall thrust of the engine.

In a conventional turbojet gas turbine, air passes through an alignedcompressor, burner and turbine and is then discharged to atmospherethrough an exhaust outlet to generate thrust. Generally, a ducted'fanengine adds the feature of taking a portion of engine air from a fanstage preceeding the low compressor and discharging it to atmosphere togenerate thrust other than through the previously mentioned exhaustoutlet. In the conventional ducted fan engine, this additional duct isof circular cross section and overlaps the engine to form an annular airpassage therebetween. With the advent of higher thrust engines, interesthas been generated in achieving a fan duct burner with performancecharacteristics satisfying requirements as regards combustionefficiency, operating range, high altitude operation, lean ignitionproperties and pressure loss.

Normally, the inlet conditions of a duct burner are such that a ductburner encounters the relatively low air temperature of a maincombustion burner and the relatively high Mach number flow of anafterburner. As a'result, the requirements of a burner located in abypass duct'cannot be satisfied by using a conventional main burner orafterburner. In this type application a conventional afterburner systemlacks the stability required for operation at relatively low inlettemperatures, the wide fuel air ratio range required, and the ability topropagate the flame across the entire duct without resultant adverseeffects on combustion efficiency. A conventional main burner wouldsuffer prohibitively high pressure losses in addition to having thedisadvantages of the afterburner system.

SUMMARY OF THE INVENTION It is a primary object of this invention toprovide a piloted flameholder construction which is primarily adaptablefor use in a ducted fan engine, the construction having favorablestability characteristics at relatively low inlet operating temperaturesand pressures; capability of operating over a wide fuel air ratio rangeand low pressure loss; and improved flame propagation through theflameholders extending across the entire duct.

In a preferred arrangement of the present invention a plurality ofcombustion zones are employed. These combustion zones are normallyannular and increase in cross-sectional area in a downstream direction.As herein illustrated, each of the combustion zones includes fuel supplymeans, air supply means and a pair of annular radially spaced walls,combustion normally occuring therebetween. In the present embodiment thegases of combustion from the first or pilot zone progress downstream tothe next combustion zone, where additional air and fuel are added tointensify the temperature of the gases coming from the pilot or initialcombustion zone, the gases generated by these zones being used with aplurality of flameholders hereinafter described.

In a preferred embodiment of the present invention, ram chutes arelocated at the sides of the second combustion zone. These ram chutesdirect air which has flowed or bypassed the pilot combustion zone intothe second combustion zone. The purpose of these chutes is to insuremixing of the second zone fuel and air mixture with the pilot zonecombustion gases. It should be understood that as many combustion zonesas desired may be employed, each zone being of substantially the sameconstruction and including fuel supply means, air supply means, radiallyspaced annular walls and ram chute mixing means.

Positioned downstream of the pilot combustion zone, and downstream ofthe second combustion zone as herein illustrated, is a plurality ofgutter-shaped flameholders. These flame-holders are positioned aroundthe circumference of the duct and are supported from the radially spacedannular walls. The flame-holders are supported from the walls such thatthe inner annular wall supports the inwardly extending flameholders andthe outer annular wall supports the outwardly extending flameholders,the flameholders thereby extending substantially across the entire duct.The construction of the flameholder and the attachment to the walls isnovel in that at the point of attachment the walls are slotted therebypermitting the hot combustion gases from within the combustion zoneannular walls to flow out and around the flameholders. The outward flowof these gases greatly increases the stability and combustion efficiencyof the flame-holders. A further embodiment of the construction of thepresent invention is to position a plurality of heat shields forwardlyor upstream of each of the flameholders. Each of the heat shields is ofsubstantially the same shape as the flameholders and effectively forms adouble-walled flameholder construction. Since the heat shields arespaced axially from the flameholders, a passageway therebetween isformed. This passageway is in communication with a combustion zonethrough the aforementioned slots in the walls, and thereby provides ameans for preheating each of the flameholders. More specifically, thehot combustion gases heat the shield affording initial vaporization offuel supplied to the flameholders from an upstream fuel supply means.Additionally, the temperature of the inner flameholders is raised; theseraised temperatures also contributing to flame-holder stability andefficiency.

The construction of the present invention further provides for increasedstability and flameholder efficiency by providing a plurality oftransfer channels extending from the pilot combustion zone to theannular walls supporting the flameholders at a point upstream of theflameholders. The exits of these transfer channels are positioned aroundthe circumference of the duct such that each exit is in substantialaxial alignment with each flameholder. Therefore, hot gases are led bythe transfer channels and issued therefrom as hot streaks over the endlocation of each of the flameholders with the hot gases flowing ontoeach of the flameholders from within the duct. This type constructionhas been found to permit favorable flameholder stability and efiiciency.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showingthe flameholder construction in longitudinal cross section.

FIG. 2 is a longitudinal cross section of the flameholder construction.

FIG. 3 is a view taken along the line 3-3 of FIG. 2.

FIG. 4 is an enlarged view of a portion of FIG. 2. showing thepositioning of a channel and flameholder along with a general flow path.

FIG. 5 is an enlarged perspective view of a portion of the inventionshowing the positioning of the channel with respect to its cooperatingflameholder.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, theconstruction of the present invention is clearly illustrated. As shown,the construction includes three combustion zones, the first combustionzone being pilot combustion zone 30 and includes any conventional fuelsupply means 12 in the burner inlet section locatedupstream of the pilotcombustion zone 30. Additionally, the inlet section 10 includes apair-of annular radially spaced walls 14 and 16, wall 14 constitutingthe inner annular wall and wall 16 constituting the outer annular wall.Walls 14 and 16 are arranged such that at their leading edges the radialspacing therebetween is relatively small so that the air flowing intoinlet section 10 is only a small percentage of the total airflow, theremainder of the air flowing around the outer surfaces of walls 14 and16.

Positioned in the radial space between walls 14 and 16 and in the burnerinlet section 10 is fuel supply means 12. As illustrated, the pilotcombustion zone 30 is formed by a pilot body 18 which is supported fromwalls 14 and 16 and includes a nose portion 20 at its leading edge. As aresult of the shape of the leading edge of the pilot body 18 and thepilot nose 20, combustion within the pilot zone occurs in a protectedregion. Also pilot body 18 includes two radially spaced walls 22 and 24,each wall having a plurality of openings 26.

It is through these latter openings 26 that a pre-mixed fuel-air mixturepasses from the inlet section 10 into pilot zone 30, these openings arethe primary means of metering the airflow to the pilot zone 30. Afterbeing burned in the pilot zone 30 these hot gases flow downstream intothe second zone 40. Combustion zone 40 is constructed in much the samemanner as pilot combustion zone 30 in that it includes fuel supply means32 positioned downstream of pilot zone 30 and surrounding the walls 14and 16 respectively. Combustion zone 40 as pilot zone 30 also includes apair of annular radially spaced walls 34 and 36.

The walls 34 and 36 are arranged such that wall 34 is the inner annularwall of combustion zone 40, the leading portion 35 thereof overlappingthe downstream portion 15 of inner wall 14 of pilot zone 30. Similarly,wall 36 is the outer annular wall of zone 40 and its leading portion 37overlaps the downstream portion 17 of wall 16. In each instance portion35 is spaced radially from portion 15 and portion 37 from portion 17 sothat two annuli exist between the pilot combustion zone 30 and thesecond combustion zone 40. Within each annulus is positioned a pluralityof scoops 41, each of the scoops facing forwardly to receive air whichhas flowed around the inlet. As shown, fuel supply means 32 arepositioned at the inlet of each of the scoops, it therefore being clearthat scoops 41 insure a proper mixing of the incoming fuel and airmixture with the combustion gases exiting from the pilot zone 30. Toinsure this proper mixing the exists 42 of the scoops 41 are arrangedsuch that they face either inwardly or outwardly. In the constructionillustrated herein, the inwardly facing exits are attached and supportedfrom the outer annular wall 36 and the outwardly facing exits areattached and supported from the inner annular wall 34. With respect tothe combustion zone 40, the scoops all face inwardly thereto. To furtherenhance mixing, either short scoops 41A or long scoops 418 may beemployed, this being more clearly illustrated in FIG. 3. It should benoted that either all long, all short, or any combination thereof may beused.

Downstream of combustion zone 40 is the third combustion zone 52.Combustion zone 52 includes fuel supply means 54 and also a plurality offlameholders 56. Flameholders 56 are positioned downstream of fuelsupply means 54, and are supported from the annular walls comprising thesecond combustion zone 40 at the downstream ends of these walls. Theflameholders 56 are arranged such that they extend radially from walls34 and 36, the flameholders supported from inner annular wall 34extending radially inward while the flameholders supported from theouter annular wall 36 extending radially outward. The flameholdersupports may be rods or any other type of fixture desired. With thistype arrangement it is possible to realize stable burning across anentire duct or opening. This can more clearly be seen in FIG. 2.

To improve the stability and the combustion efficiency of theflameholders the present invention provides a number of unique features.As illustrated in the present embodiment, gases from the pilot zone 30move downstream and are mixed with the air and fuel entering the secondcombustion zone 40 the heat and temper thereby being intensified. Toutilize these hot combustion gases which have been generated in thefirst two combustion zones, the annular walls 34 and 36 are slottedaround their entire circumference, as at 60 to permit passage of thesegases to the flame-holders 56. In the present embodiment flameholders56, which are gutter-type flameholders which are substantially U- shapedin cross section with the apex of the U facing upstream, are positionedover slots 60 such that the generated combustion gases may pass alongand radially out the upstream and downstream sides of the flameholders56. A flameholder support could include integral fingers projecting fromits open end of the U to its flameholder. To further enhance theperformance characteristics of the flame-holders 56, a plurality of heatshields 62 positioned forwardly of and axially spaced from each of theflameholders 56 may be employed. Each of the heat shields 62 issubstantially the same shape as its associated flameholder, soeffectively the construction is a double-walled construction with apassageway 64 therebetween.

FIG. 3 illustrates an additional feature which also improves theperformance characteristics of flameholders 56. A plurality of transferchannels 66 are employed, one end 68 of each of the channels being incommunication with the gases generated in the two combustion zones andeach of the other ends 70 being arranged around the circumference ofannular walls 34 and 36. These transfer channels are located between thedownstream portion l5 of inner wall 14 and the leading edge portion 35of wall 34 and between the downstream portion 17 of wall 16 and theleading portion 37 of wall 36. The ends 68 of the channels 66 can beconsidered the inlet ends of the channels and the ends 70 of thechannels can be considered the exit ends of the channels, in that gasesgenerated flow outwardly from end 68 to end 70 to the inside of walls 34and 36 where they then flow downstream. The exits 70 of transferchannels 66 are further arranged such that each exit 70 is substantiallyaxially aligned with each of the flameholders 56. Therefore, as the hotcombustion gases issued from the exits 70, they do so as hot streakswhich travel along walls 34 and 36 and onto each of the flameholders 56.

in FIG. 2 the present invention is illustrated as being positioned in anannular duct 80, concentric wall 72 being the inner wall of duct 80 andconcentric wall 74 being the outer wall of duct 80. Each wall hassimilar flange means 76 for attachment to an engine (not shown).

it is to be understood that the invention is not limited to the specificembodiments herein illustrated and described but may be used in otherways without departure from its spirit as defined by the followingclaims.

We claim:

1. A piloted flameholder construction including a plurality ofcombustion zones, each zone having means for supplying fuel and airthereto for combustion, wherein the improvement comprises:

supporting a plurality of flameholders rearwardly of at least the firstcombustion zone; and

means for supplying hot combustion gases from at least one of thecombustion zones to apoint forwardly of each of the flameholders, eachof these points being in substantially axial alignment with each of theflameholders, the combustion gases exiting from each of these points asa hot streak and being directed at and onto each of the flameholders.

2. A flameholder construction as in claim 1, wherein:

and the flameholders extend radially inwardly and outwardly from thesewalls. 3. A flameholder construction as in claim 2, wherein:

the means for supplying hot combustion gases includes a plurality oftransfer channels extending from at least one combustion zone to a pointforwardly of the flameholders, each of the channels having an exit whichis substantially axially aligned with a flameholder.

4. A piloted flameholder construction including a plurality ofcombustion zones, each zone having means for supplying fuel and airthereto for supporting combustion at each zone, wherein the improvementcomprises:

a first combustion zone including a first pair of radially spacedannular walls, the upstream ends of the spaced walls constituting theburner system inlet,

this first combustion zone including a protected region bounded by asecond pair of radially spaced annular walls inside the first pair ofwalls, means for permitting a predetermined amount of air to pass intothis pilot combustion zone, the remainder of the airflow passing aroundthe inlet of the burner system;

a second combustion zone downstream of the first combustion zoneincluding a third pair of radially spaced annular walls, the third pairof annular walls being radially spaced from the first pair of walls;

a plurality of scoops positioned between the two pairs of annular walls,each of the scoops having exit locations directed either inwardly oroutwardly, the inlets of the scoops facing forwardly to receive the airflowing past the first combustion zone;

a plurality of transfer channels extending between the first combustionzone and the second combustion zone, the transfer chennels permittingpassage of hot combustion gases from the first combustion zone to theexit of each of the transfer channels; and

a third combustion zone downstream of the second combustion zoneincluding a plurality of guttershaped flameholders, each of theflameholders being substantially in axial alignment and downstreamthereof of the exits of each of the transfer channels, a hot gas streakissuing from the exit of each of the transfer channels and beingdirected at each of the flameholders.

5. A flameholder construction as in claim 4 wherein:

the third pair of walls support the flameholders, the walls beingslotted at the point of support of each of the flameholders to permitpassage of hot combustion gases from the second combustion zone alongeach of the flameholders.

6. A flameholder construction as in claim 5 wherein:

a plurality of heat shields of substantially the same cross section aseach of the flameholders is spaced axially therefrom and at the leadingedge of each of the flameholders, the hot combustion gases from thesecond combustion zone being passed through the slots between each ofthe heat shields and flameholders and around the flameholders.

7. A flameholder construction as in claim 6 wherein:

the heat shields and the flameholders are substantially U-shaped, andthe apex of the U of the heat shield and flameholder is facing upsteam.

8. A flameholder construction as in claim 5 wherein:

the flameholders supported from the inner annular wall extend radiallyinward therefrom and the flameholders supported from the outer annularwall extend radially outward therefrom.

9. A piloted flameholder construction for use with a ducted fan gasturbine engine, the flameholder being positioned in the relatively coolfan gas stream and including a plurality of combustion zones, each ofthe zones having means for supplying fuel and air thereto for supportingcombustion in each zone, wherein the improvement comprises:

an outer concentric wall including means for connecting the wall to theengine;

an inner concentric wall spaced radially inward one of the combustionzones also including a pair of annular radially spaced walls, theflameholders being supported from both of the walls, the flameholdersextending radially inwardly and outwardly from the wall therebyextending substantially across the entire duct; and

means for supplying hot combustion gases from at least one of thecombustion zones to a point forwardly of each of the flameholders, eachof these points being in substantially axial alignment with each of theflameholders, the combustion gases exiting from each of these points asa hot streak and being directed at and onto the base of each of theflameholders.

10. A flameholder construction as in claim 9 wherein:

there are three combustion zones and the flameholders are positioneddownstream of the second combustion zone and the third combustion zoneincludes means for conducting hot combustion gases around each of theflameholders thereby heating each of the flameholders.

l l. A piloted flameholder construction as in claim 10 5 wherein:

each of the flameholders are gutter-shaped and a heat shield ofsubstantially the same construction is positioned forwardly of each ofthe flameholders, each of the heat shields and flameholders therebyhaving a space therebetween, this space being in communication with oneof the preceeding combustion zones thereby permitting a flow of hotcombustion gases between the heat shields and the flameholders.

12. A piloted flameholder as in claim 11 wherein:

the heat shields and the flameholders are substantially Ushaped, and theapex of the U of the heat shield and flameholder is facing upstream.

13. A piloted flameholder construction as in claim 10 wherein:

the means for supplying the hot combustion gases includes a plurality oftransfer channels each of the channels extending from the secondcombustion zone to a point forwardly of each of the flameholders.

1. A piloted flameholder construction including a plurality ofcombustion zones, each zone having means for supplying fuel and airthereto for combustion, wherein the improvement comprises: supporting aplurality of flameholdErs rearwardly of at least the first combustionzone; and means for supplying hot combustion gases from at least one ofthe combustion zones to a point forwardly of each of the flameholders,each of these points being in substantially axial alignment with each ofthe flameholders, the combustion gases exiting from each of these pointsas a hot streak and being directed at and onto each of the flameholders.2. A flameholder construction as in claim 1, wherein: the combustionzones include a pair of annular radially spaced walls each of theflameholders being supported from at least one of these pairs of walls,and the flameholders extend radially inwardly and outwardly from thesewalls.
 3. A flameholder construction as in claim 2, wherein: the meansfor supplying hot combustion gases includes a plurality of transferchannels extending from at least one combustion zone to a pointforwardly of the flameholders, each of the channels having an exit whichis substantially axially aligned with a flameholder.
 4. A pilotedflameholder construction including a plurality of combustion zones, eachzone having means for supplying fuel and air thereto for supportingcombustion at each zone, wherein the improvement comprises: a firstcombustion zone including a first pair of radially spaced annular walls,the upstream ends of the spaced walls constituting the burner systeminlet, this first combustion zone including a protected region boundedby a second pair of radially spaced annular walls inside the first pairof walls, means for permitting a predetermined amount of air to passinto this pilot combustion zone, the remainder of the airflow passingaround the inlet of the burner system; a second combustion zonedownstream of the first combustion zone including a third pair ofradially spaced annular walls, the third pair of annular walls beingradially spaced from the first pair of walls; a plurality of scoopspositioned between the two pairs of annular walls, each of the scoopshaving exit locations directed either inwardly or outwardly, the inletsof the scoops facing forwardly to receive the air flowing past the firstcombustion zone; a plurality of transfer channels extending between thefirst combustion zone and the second combustion zone, the transferchennels permitting passage of hot combustion gases from the firstcombustion zone to the exit of each of the transfer channels; and athird combustion zone downstream of the second combustion zone includinga plurality of gutter-shaped flameholders, each of the flameholdersbeing substantially in axial alignment and downstream thereof of theexits of each of the transfer channels, a hot gas streak issuing fromthe exit of each of the transfer channels and being directed at each ofthe flameholders.
 5. A flameholder construction as in claim 4 wherein:the third pair of walls support the flameholders, the walls beingslotted at the point of support of each of the flameholders to permitpassage of hot combustion gases from the second combustion zone alongeach of the flameholders.
 6. A flameholder construction as in claim 5wherein: a plurality of heat shields of substantially the same crosssection as each of the flameholders is spaced axially therefrom and atthe leading edge of each of the flameholders, the hot combustion gasesfrom the second combustion zone being passed through the slots betweeneach of the heat shields and flameholders and around the flameholders.7. A flameholder construction as in claim 6 wherein: the heat shieldsand the flameholders are substantially U-shaped, and the apex of the Uof the heat shield and flameholder is facing upsteam.
 8. A flameholderconstruction as in claim 5 wherein: the flameholders supported from theinner annular wall extend radially inward therefrom and the flameholderssupported from the outer annular wall extend radially outward therefrom.9. A piloted flameholder construction for use with a ducted fan gasturbine engine, the flameholder being positioned in the relatively coolfan gas stream and including a plurality of combustion zones, each ofthe zones having means for supplying fuel and air thereto for supportingcombustion in each zone, wherein the improvement comprises: an outerconcentric wall including means for connecting the wall to the engine;an inner concentric wall spaced radially inward therefrom and alsoincluding means for connecting the wall to the engine, the two wallsforming a duct therebetween within which the plurality of combustionzones are positioned, the combustion zones being arranged so that eachsuccessive downstream zone can accommodate a greater amount of flow thanthe zone immediately upstream; one of the combustion zones alsoincluding a pair of annular radially spaced walls, the flameholdersbeing supported from both of the walls, the flameholders extendingradially inwardly and outwardly from the wall thereby extendingsubstantially across the entire duct; and means for supplying hotcombustion gases from at least one of the combustion zones to a pointforwardly of each of the flameholders, each of these points being insubstantially axial alignment with each of the flameholders, thecombustion gases exiting from each of these points as a hot streak andbeing directed at and onto the base of each of the flameholders.
 10. Aflameholder construction as in claim 9 wherein: there are threecombustion zones and the flameholders are positioned downstream of thesecond combustion zone and the third combustion zone includes means forconducting hot combustion gases around each of the flameholders therebyheating each of the flameholders.
 11. A piloted flameholder constructionas in claim 10 wherein: each of the flameholders are gutter-shaped and aheat shield of substantially the same construction is positionedforwardly of each of the flameholders, each of the heat shields andflameholders thereby having a space therebetween, this space being incommunication with one of the preceeding combustion zones therebypermitting a flow of hot combustion gases between the heat shields andthe flameholders.
 12. A piloted flameholder as in claim 11 wherein: theheat shields and the flameholders are substantially U-shaped, and theapex of the U of the heat shield and flameholder is facing upstream. 13.A piloted flameholder construction as in claim 10 wherein: the means forsupplying the hot combustion gases includes a plurality of transferchannels each of the channels extending from the second combustion zoneto a point forwardly of each of the flameholders.